1. Field of the Invention
This invention relates in general to treadmills and in particular to an improved shock absorbing treadmill which provides in use reduced landing forces to a runner's foot while simultaneously providing a substantially flat, stable running surface.
2. Description of the Prior Art
The art has provided treadmills in response to demand of walkers, joggers and runners and the medical profession for a device which may be used, especially indoors, for exercise where outdoor walking, jogging or running is not enjoyable or practical. A problem with running or jogging as an exercise to strengthen the cardiovascular system relates to the possibility of impact injury to feet, ankles and knees caused by the force of the runner's foot striking an unyielding surface, such as street pavement. Prior treadmill designs have recognized this problem and have attempted to solve it in a number of ways. For example, U.S. Pat. No. 4,614,337 of Schomenberger discloses a treadmill with a flat top surface covered with a resilient surface such as foam rubber, carpeting or the like. Another example is U.S. Pat. No. 4,548,405 to Lee et al which discloses a trampoline like top surface for a treadmill.
U.S. Pat. No. 4,350,336 to Hanford provides a treadmill having a frame to which rollers are attached which carry an endless tread belt. The belt moves above a platform disposed beneath the running portion of the belt. The platform is supported by longitudinal platform rails which are supported at one end by a lateral frame member which is secured to the frame. The platform is supported at its other end by shock absorbing members attached to the longitudinal rails. The shock absorbing member may be moved longitudinally with respect to the frame. The shock absorbing member absorbs shock directly of the platform as a runner exercises on the treadmill belt above. The platform flexes longitudinally as it pivots at one end and is shock absorbingly supported at its other end.
Although an admirable improvement in the art of shock absorbing treadmills, the Hanford treadmill does not provide an adequately stable running surface. The platform is shock absorbingly supported, but the endless tread belt is not. The belt rollers are both supported directly by the frame. As a result, the belt runs over the platform with sufficient slack in it to allow the platform beneath it to move downwardly in response to the impact of a runner's foot. The slack in the belt can cause an uneven lateral surface for succeeding foot landings, possibly leading to twisted ankles, knees, etc.